Saab 37 Viggen

[Viggen on approach]
Photo by Bernt Törnell
Viggen is a multi-role fighter, through upgrades still modern and with some almost unique features, in service with the Swedish air force in several versions, since 1971 and until after 2006. The name Viggen means The Thunderbolt, especially those resulting from the Norse god Thor's warhammer Mjölner.

In 1952 studies were started to design a replacement for Saab Draken. "Project 1357" in 1954, was the first to have a canard layout (lots of other layouts were studied as well). I n 1961, P&W JT8D-22 was the chosen engine to be locally built, with a locally designed afterburner and lots of material changes in the rest. In 1962 the design was frozen, and the prototype first flew in Feb 8:th 1967. During the 1960's, it was foreseen that the Swedish air force would purchase 800+ Viggens, but the final figure ended up at 329.

In order to make the airframe smaller, it was early decided to replace the navigator with a good navigational computer. It's designed to withstand 12 G, but the limit in operation is 7 G.

The seat in angled back 19 degrees.

Emergency power is supplied by a ram air turbine just before the left wing leading edge, which extends automatically on hydraulic power failure, and just before touch down. (Earlier, it was also always deployed whenever the landing gear was down.)

The canard doesn't contribute much lift in itself during normal flight, it acts more as a gigantic vortex generator for the main wing. During low speed flight, its rear edge flap can be lowered to increase lift and permit a high nose angle.

The requirement was that the aircraft would be able to operate from 500 m runways. A short take-off run is possible due to the powerful engine (then, it was the most powerful installed in a fighter).

Landing distance is reduced by several means: The HUD is used as a precision landing aid, making it possible to aim just 30 m in from the threshold; The landing gear thinks a landing sink rate of 5 m/s is normal, so landings are done without any flare; The thrust reverser is interconnected with the nose gear link, so it can be selected in the air and will operate when the nose is lowered. (It is not intended to be used in the air.)

The aircraft must be servicable very quickly by concripts with relatively short training. Re-fueling and re-arming by 7 men, of which 6 are concripts, must take less than 10 min for the JA 37 Viggen. The time limits for reconnaissance and attack configured aircraft are 15 and 20 minutes.

It is said that attack squadrons expect to fly 11 missions per aircraft and 24-hour period. 

Designations
A, Attack                   = Strike
Sk, Skol                    = Training
SF, Spaning Foto            = Reconnaissance Photo
SH, Spaning Havsövervakning = Reconnaissance Maritime surveillance
J, Jakt                     = Fighter
When two or more designations are combined, the first 
denotes primary role.

Variants

[Bare metal Viggen] AJ 37 Viggen

108 delivered starting in 1971, remained in more or less original form until about 1998, but were converted to the AJS 37 standard starting a few years before that. Last operational flight was in March 2000. Serial numbers 37001-37108.

This is the strike variant. When it was designed, guns were definitely passé, so there was no provision made for an internal cannon. Dumb bombs weren't popular either, so during the preliminary design stages, the only armament considered were missiles. It wasn't until the prototypes were actually in progress of beeing built, that someone thought of incorporating wiring for iron bombs, presumably as it was realised the HUD/Weapons Aiming Computer system would enable them to be dropped with good precision.

Main armament for the anti-shipping role, a very important role, is the Saab 304 rocket-powered anti-ship missile. For ground attack, 135 mm Bofors M70 rockets (either 21 kg GP warhead with 3.7kg explosive or 20 kg AP fragmentation warhead with 5 kg explosive) in pods of six each, were together with the command controlled, smoke-less liquid fuel Saab 305 missile, the main weapons, with the 120 kg bombs and 30 mm podded guns used when appropriate.

The Saab 305/Rb 05 missile is now an all round weapon, as it is rather effective against slow, large aircraft and helicopters too. A TV version was contemplated as the Rb 05B, but it was cheaper to buy Mavericks instead.

It has always had a secondary fighter role, with Sidewinders and 30 mm cannon in pods.

In service, it replaced the A 32A Lansen.


[SK 37 from rear] Sk 37 Viggen

17 delivered starting in 1973, will remain in service for a long time yet, some converted to SK 37E ECM aggressor standard. Serial numbers 37801-37817.

To make room for the second cockpit, fuel and avionics was removed, so it has a shorter range and lacks a radar. The fin is taller. The rear cockpit has two periscopes to give forward vision.

[SK 37 cockpits] The trainer version wasn't planned from the outset, as it was considered enough for pilots to learn to fly delta winged aircraft on Draken trainers.

SK 37E


Photo by Niklas Knutzén
To replace J 32E Lansens in the ECM role, ten two seat Viggens will be modified for that role and designated SK 37E. The first of them will be delivered late in 1998.

Apart from the [aggressor squadron] ECM role, they will be used for conversion training and be based at the F 4 wing at Östersund, where the SK 37s transferred after the F 15 wing was disbanded.

About it at F 4's web site: SK 37E Viggen - text in Swedish, but there's photos of the equipment.


[SH 37 with camera pod] SH 37 Viggen

27 delivered between 1975 and 1980, remained in service in original form until around 1998, as conversion to the AJSH 37 standard started a few years earlier. At the end of 2003 they will be retired. Serial numbers 37901-37927.

During the early design process, it was envisioned to have both cameras and radar in the same airframe, but that proved to take up too much space, so separate versions had to be developed.

The radar has better range than AJ 37, as well as a recorder.

A long focal length forward looking SKa 24D-600 is semi-permanently mounted on the right fuselage station, to register what's been seen on the radar and to take other photos.

During a period the wing F 13 used two Recon/Optical CA-200 1676 mm cameras inside rebuilt centre line fuel tanks.

In service it replaced the S 32C Lansen 

The fuselage pylons look like this      As compared to this on the attack
on the recce versions                   and fighter version

/ | \                                  /  |  \
/  |  \                                 |  |  |

[Photo reconnaissance Viggen] SF 37 Viggen

28 delivered between 1977 and 1980, in original form until around 1998, as conversion to the AJSF 37 standard started a few years earlier. Will be retired in 2006 when Gripen has gotten an optical reconnaissance pod. Serial numbers 37950-37977. [Camera sight close up] All fixed cameras are carried in the nose, that lacks a radar. [SF 37 from the front] There are three SKa 24C-120 for horizon-to-horizon coverage, an SKa 24-57 for wide angle pictures and two SKa 31-600 for high altitude or stand off photography. There is also an IR-linescan designated VKA 702.

[Right hand side pod] [Left hand side pod] For night photography, a pod is carried on the left fuselage station, with three SKa 34-75 cameras loaded with IR sensitive film in the front. The rear of the pod houses electronic IR flashes, as does a complementary pod on the starboard fuselage station.

In service it has replaced the S 35E Draken.

[Fighter Viggen] JA 37 Jaktviggen

149 delivered between 1979 and 1990, will be retired by 2004. Serial numbers 37301-37449.

By the time this version was in final design, it was clear that guns were definitely useful, so it was given the most powerful cannon a fighter has had, a 30 mm Oerlikon KCA with 150 rounds. Rate of fire is 22.5 0.36 kg rounds/s at 1050 m/s, which gives them six times more kinetic energy than the 30 mm Adens on the attack version.

A unique feature is the coupling of the radar gunsighting mode to the autopilot, introduced with Edit 32. When the pilot places a target in a capture window, the autopilot takes over pitch and yaw, and presents bank information on the HUD for the pilot to follow. Even if it's not followed, the pitch and yaw channels have enough authority to precision aim the cannon, reducing pilot workload letting him or her concentrate on tactics and situational awareness.

The fighter version has an inertial navigation system instead of the earlier versions' doppler navigation system. It is 13 cm longer, partly because the RM8B engine, which is smokeless, more powerful and better suited to high altitude than the RM8A which powers the other Viggen versions, is 8 cm longer than the RM8A. There is a three stage fan, three stage LP compressor and a seven stage HP compressor, as compared to 2/4/7 on RM8A.

The fin is the same tall one as on Sk 37 to compensate for the longer fuselage. The external tank is the same size as on the other versions, but because there's a bulge where the gun is installed, there is no room for the abbrevited top fin of the tank, instead of three fins, this tank has four fins, in a flattened 'X'.

In spite of having a strengthened wing, an engine 100 kg heavier (2200 kg) and a fixed cannon, it only has an empty weight 400 kg more than earlier versions.

In service it has replaced and supplemented the J 35 Draken.

JA 37 upgrades

The system has gone through numerous upgrades since service entry. The radar is able to track more targets now, than at service entry, for example. (In the late 1980's it was revealed that the capability to track two target while scanning had been introduced, and hinted at that as hardware got cheaper, more was a strong possibility.)

*
Photo by Martin Rosenkranz, Fairford 1999.
The lastest software upgrade, EDIT 34, enables the JA 37 to use AMRAAM missiles. A trials aircraft started flying with it in the autumn of 1997.

This modification package, called "D", also requires some hardware updates to the aircraft, is being introduced in series aircraft from the summer of 1998, and apart from the AMRAAM compatibility also includes a weapons interface like Gripen's, the new radio TARAS, improved cockpit and computers as well as ECM. Upgrade of simulators is also included.

Edit 32, in 1993, mainly introduced advances in the flight control system and radar. Many of the hardware advances needed for Edit 32, "Modification package C", were introduced at the same time as Edit 30, in 1990, but not put to full use. One example is the upgraded radar signal processor, which now has much better ECCM, among other things.

U95 has one pointed radome at the front and a blunt at the rear, as well as two strakes along the sides. Mod D includes the ability to carry the Ericsson Saab Avionics U95 countermeasures pod.

One other radar function added with Edit 32 is the possibility to generate virtual targets. Saves money as some exercises can be done with fewer aircraft, but also allows exercises which from a safety standpoint would be unsuitable during peace time training.

One flight control improvment is a better autothrottle, which now behaves "more like a pilot would" and also takes into account more aircraft parameters.

AJS 37 Viggen

Starting in 1992, 115 AJ, SF and SH 37 Viggens were rebuilt to AJS 37 standard.

[RBS 15F] One reason for the upgrade is to take advantage of the weapons, specifically the RBS 15F anti-ship missile and [Mjölner] Mjölner bomblet dispenser, already ordered and in production for Gripen, it was decided to modify a number of earlier Viggens, to make them truly multi-role.

The modification will be in two stages, the ability to carry AIM-9Ls didn't arrive until 1996.

Not all AJ/SH/SF were modified, as there was no life extension involved, and the first AJ 37s were retired soon after Gripen entered service.

"Ex AJ 37" AJS 37s were never meant to carry cameras, but will perform radar reconnaissance missions. Initial plans were ambitious, but for economic reasons the SF 37s weren't modified to fulfil the ground attack role, and the radar related hardware (switches, displays) in the AJ and SH 37s will remain as before the modification, so each subvariant of AJS 37 got its own designation:
AJ 37 -> AJS 37
SH 37 -> AJSH 37
SF 37 -> AJSF 37

Prototypes

There have been 14 prototypes, of which 5 were rebuilds of other aircraft. One aircraft was lost before delivery, and is not included in the above.

Scrapping

Retired Viggens have been scrapped at Ängelholm since 1993. By mid-2000 about 100, including ten JA 37s had been scrapped.

Scrapping an AJ/S 37 takes four weeks, the more technically advanced JA 37 six weeks, as it's done carefully in order to use as much as possible for spare parts. Of the electronic parts taken out of a JA 37, up to 80% is in use in another aircraft within a month, and for example the backup artificial horizon gyro can be used in SK 60, but not only electronics is reused.

SWEFRAP AJS 37

The Swedish air force has two units for international missions, Swedish Air Force Rapid Reaction Unit C-130 and AJS 37.

The AJS 37 unit consists of AJSF 37 Viggens and its mission will be photo reconnaissance in conflict areas. Currently (2000) it can be operational 90 days after decision, by 2001 it will be available in 30 days, and a planning group will be able to leave Sweden within 15 days to make preparations.

In 2004 the unit was replaced by a JAS 39 Gripen unit.

[Attack Viggen with lots of different weapons on the ground] Armament options

[Diagram showing all AJ 37 options] Photo shows AJ 37 Viggen with 120 kg bombs loaded, Rb 05 missile (green) Rb 04E (black and white), 30 mm gun pods and 135 mm rocket pods.

Diagram shows all weapon load alternatives for AJ 37 Viggen cleared for use in 1979. 

         |
         |
    ____/n\____
_______[(.)]_______

 8 6 4 2 1 3 5 7 9      The stations are numbered thus

AJ 37

         T              External tank (1400? litre)
   R   R   R   R        6 x 135 mm M70 rockets (364 kg)
   B   B   B   B        4 x 120 kg M63FFV fragmentation bombs, Sprängbomb m/71 Virgo
   I   I   I   I        4 x 80 kg illumination flares
   04    04    04       Rb 04E, Saab 304, 620 kg rocket anti-ship missile
   U22                  Erijammer 200 ECM pod (350 kg) (Previously known as KA,
                        for "pod type A")
               KB       BOX-9 chaff/flare dispenser (325 kg) (KB = "pod type B")
   75          75       Rb 75/75T Maverick. 75 = AGM-65A, 210 kg, 75T (T for "heavy") = AGM-65A with blast warhead, 295 kg.
       05  05           Rb 05, Saab 305 command controlled missile (305 kg)
                        usable against ground and slow air targets
   G           G        30 mm Aden cannon with 150 rounds (364 kg)
       24  24           Rb 24/24J Sidewinder

28                28    RB 28 Falcon (IR). The initial AAM selected for Viggen. Not used
                        because its long warm up period. The pylon not used because a missile
                        there causes too much vibration on an AJ 37. (Stations 8/9 not normally used 
                        on AJ/S 37 due to the vibration issue.)
AJS 37
24 24  24  24  24 24    Rb 24/24J Sidewinder 
   74  74  74  74       Rb 74 (AIM-9L) Sidewinder (1996 and later)
   15          15       Rb 15F jet powered anti-ship missile (598 kg)
   BK  BK  BK  BK       Bombkapsel m/90, Mjolner. Gliding bomblet dispenser.
   75  75  75  75       Rb 75 (AGM-65) Maverick (210 kg)
   05  05  05  05       Rb 05, command controlled missile (305 kg)
   G           G        30 mm Aden cannon with 150 rounds (364 kg)
   R   R   R   R        6 x 135 mm M70 rockets (364 kg)
   B   B   B   B        4 x 120 kg M63FFV fragmentation bombs
   I   I   I   I        4 x 80 kg illumination flares
  TSA         TSA       "Heavy guided stand-off weapon" (none selected or included in the budget
                        although something in the GBU-15 class was envisioned already in the
                        early 1980's).
   R   R   24  R        Note that assymetric loads like can be used
-----
SK 37                   Lacks a radar, so its weapons are limited to:
         T              External tank
   R   R   R   R        6 x 135 mm M70 rockets (364 kg)
   G           G        30 mm Aden cannon with 150 rounds (364 kg)

SK 37E
               U95      ECM pod, not certain if this and the U22/A can be under either wing
   U22/A                ECM pod
   KB          KB       Chaff and flare dispenser
BT                53    Saab BT-53 laser reflector
-----
SH 37
         T              External tank
       FC               Forward looking 600 mm camera in
   U22                  Erijammer 200 ECM pod (350 kg)
               KB       BOX-9 chaff/flare dispenser (325 kg)
           24           Rb 24/24J Sidewinder
       C   C            Port station: 3 IR film cameras, electronic IR flashes
                        in the rear, starboard IR flashes only.
   04          04       Rb 04E, 620 kg rocket powered anti-ship missile

AJSH 37
24 24  24  24  24 24    Rb 24J Sidewinder
   74  74  74  74       Rb 74 (AIM-9L) Sidewinder (1996 and later). Air cooled.
   15          15       Rb 15F jet powered anti-ship missile (598 kg)
   BK  BK  BK  BK       Bombkapsel m/90, Mjolner. Gliding bomblet dispenser.
   G           G        30 mm Aden cannon with 150 rounds (364 kg)
   R   R   R   R        6 x 135 mm M70 rockets (364 kg)
   B   B   B   B        4 x 120 kg M63FFV fragmentation bombs
   I   I   I   I        4 x 80 kg illumination flares
( TSA         TSA       Tungt Styrt Attackvapen = "Heavy guided stand-off weapon" 
                        Not yet funded for Gripen, so won't be used on Viggen)
                        
-----
SF 37
         T              External tank
       C   C            Port station: 3 IR film cameras, electronic IR flashes
                        in the rear, starboard IR flashes only.
   U22                  Erijammer 200 ECM pod (350 kg)
               KB       BOX-9 chaff/flare dispenser (325 kg)
       24  24           Rb 24/24J Sidewinder

AJSF 37
24 24  24  24  24 24    Rb24/Rb 24J Sidewinder
   74  74  74  74       Rb 74 (AIM-9L) Sidewinder (1996 and later)
-----
JA 37
                        Built in 30 mm Oerlikon KCA with 150 rounds
         T              External tank, with four fins
24 24  24  24  24 24    Rb 24J Sidewinder
74 74  74  74  74 74    Rb 74 (AIM-9L) Sidewinder
   71          71       Rb 71 SkyFlash
   R   R   R   R        6 x 135 mm M70 rockets (364 kg) for ground attack
     F       F          BOY 401 flare launcher (12x2 each) Countermeasures dispensers

JA 37D
 C                C     BOL 451 chaff launcher/missile rail (LAU-138)
74 99  99  99  99 74    With EDIT 33, RB 99, Amraam will also be carried
   U95                  U95 countermeasures pod (almost as Erijammer A110)

Technical data


                  AJ/SH     SF        SK        JA
Take off run:     400 m     400 m     400 m     400 m
Landing run:      450 m     450 m     450 m     450 m 
Landing speed:    220 km/h  220 km/h  220 km/h  220 km/h
Length:           16.30 m   16.50 m   16.30 m   16.43 m
Span:             10.6 m    10.6 m    10.6 m    10.6 m
Height:            5.6 m     5.6 m     5.6 m     5.9 m
 w folded fin:     4.0 m     4.0 m     4.0 m     4.0 m
Engine thrust:    6690 kp   6690 kp   6690 kp   7415 kp
 w afterburner:  11790 kp  11790 kp  11790 kp  13125 kp
Range:            2000 km   2000 km             2000 km
   Ferry range would be 2250 km, about 15-16% more with Jet A1 fuel.
Empty weight:     9500 kg   9500 kg             9500 kg
Max payload:      3600 kg   2500 kg             1700 kg
 (excluding external tank)
Max take off                             
 weight:         18000 kg  17000 kg            18600 kg
Max speed                                (at 3600 kg load?)
 low altitude:  Mach 1.1   Mach 1.1           Mach 1.2
 high altitude: Mach 2+    Mach 2+            Mach 2+
Guaranteed speed
 high altitude: Mach 1.7   Mach 1.7           Mach 1.8
Time from brake release to 10 km or Mach 1 at low altitude: 100 s
Max altitude:    18000 km   18000 m            18000 m
[Air Power Journal, Summer 1993, various issues of FlygvapenNytt and other Swedish air force informational material]

Related subjects

Swedish military aircraft descriptions
More on military aviation
Text last updated 1997 March 05, except for small changes, document last modified 2004 Oct 29 by Urban Fredriksson
Top photo by Bernt Törnell, U95 photo provided by Ericsson Saab Avionics, SK 37E photo by Nicklas Knutzén, the rest by me, 1975 and later.
griffon@canit.se